Debian-Pi-Aarch64/docs/uboot.md

build

wget https://source.denx.de/u-boot/u-boot/-/archive/v2021.04/u-boot-v2021.04.tar.gz
cd  u-boot-v2021.04/
make distclean
make rpi_4_defconfig
make -j X
cp u-boot.bin /boot/

config.txt

add:

kernel=u-boot.bin
kernel_address=Ox00080000
arm_64bit=1
enable_uart=1
uart_2ndstage=1
enable_gic=1

PS:

kernel=kernel8.img change to kernel=u-boot.bin